Directed evolution of Vibrio fischeri LuxR signal sensitivity

LuxR is the core component of Vibrio fischeri quorum sensing. It acts as the transcriptional activator by binding to its cognate signaling molecules 3-oxo-hexanoyl-homoserine lactone (3OC6HSL). Although several acyl-HSLs with 3-oxo groups are known to activate LuxR with similar efficiency, acyl-HSLs without 3-oxo groups are very weak inducers. We conducted a round of LuxR directed evolution to acquire LuxR mutants with higher signal sensitivity to octanoyl-homoserine lactone (C8HSL). All of the isolated mutants showed increased signal sensitivity to many other acyl-HSLs, including C8HSL, and some to the LuxR antagonist p-coumaroyl-HSL. The evolution of their ligand sensitivity proceeded through the stabilization of the signal-bound state, thereby elevating the effective concentration of LuxR at the ON-state.